Methods relating to microsurgical robot system

ABSTRACT

A method of operating a surgical system. The method includes obtaining a magnetic resonance imaging (MRI) scan in which magnetic resonance (MR) visible targets are located; registering a robotic arm to the MRI scan using a digitizing tool, the robotic arm including: multiple joints and multiple degrees of freedom; an MR-compatible structural material; multiple MR-compatible joint motors; multiple MR-compatible joint encoders; and an end effector holding an MR-compatible surgical tool having a tool tip; and displaying a location of the tool tip relative to an image from the MRI scan.

CROSS REFERENCES TO RELATED APPLICATIONS

This patent application is a continuation of co-pending application Ser.No. 11/480,701 filed on Jul. 3, 2006, which is a continuation ofapplication Ser. No. 10/639,692 filed on Aug. 13, 2003, now U.S. Pat.No. 7,155,316, which claims priority to U.S. Provisional PatentApplication No. 60/402,724 filed on Aug. 13, 2002; each of theseapplications is incorporated by reference in its entirety. This patentapplication is also co-pending with application Ser. Nos. 11/562,768filed on Nov. 22, 2006 and 11/735,983 filed on Apr. 16, 2007.

BACKGROUND OF THE INVENTION

Complication avoidance in microsurgery (neurosurgery, opthalmology,otorhinolaryngology, limb and digit reattachment) is crucial, andminimizes patient morbidity and health care costs. Current operativetechniques rely on human surgeons, who have variable skill anddexterity. They also have physiological limits to their precision,tactile sensibility and stamina. Furthermore, the precise localizationof brain pathology and neural structures is often difficult to achieveduring surgery due to brain shifts and deformations as the operationprogresses. While Intra-operative Magnetic Resonance Imaging (iMRI) hasbeen used to monitor brain deformations, the surgeon currently has noeffective way to use the iMRI data to enhance the precision anddexterity of surgery. They are compelled to rely on old techniques, anddo not take advantage of these exquisite, updated images. Consequently,the quality of the surgery and outcomes is variable, and too oftensub-optimal.

Surgical robots have the potential to increase the consistency andquality of neurosurgery, and when used in conjunction with the advanceddiagnostic imaging capabilities of iMRI, can offer dramaticimprovements. Unfortunately, there are no surgical robots that providethe surgeon with an ambidextrous and precise surgical system that usesupdated iMRI patient data to achieve accurate image-guided surgery. Inaddition, there is no surgical robot with force sensing technology thatis compatible with MRI systems.

Traditional surgery relies on the physician's surgical skills anddexterity and ability to localize structures in the body. Surgicalrobots have recently been developed to address the physical human issuessuch as fatigue and tremor in procedures. These systems werespecifically developed for Minimally Invasive Surgery (MIS) or“key-hole” general surgery, orthopaedics and stereotactic neurosurgery.

The Intuitive Surgical Inc. DA VINCI® and Computer Motion ZEUS® robotsare examples of MIS robots. MIS robots are not suitable for neurosurgerysince they require a portal in the body and lack the required dexterityand ability to reposition to different surgical worksites. Furthermore,neither system is MR compatible nor is there any force feedbackcapability. One patent on this development is U.S. Pat. No. 6,394,998 ofWallace et al issued May 28^(th) 2002.

The DA VINCI® system is archetypal for general surgical robots. It hasan articulated ENDOWRIST®, at the end of its two 7 mm diameter ‘working’arms. A more stable camera arm with two lenses (allowing stereoscopicimages) is also inserted through an 8 mm portal. The end-effectors canmanipulate instruments with tips as small as 2 mm. They have sevendegrees of freedom (three at the wrist). The surgeon controls the robotthrough a console placed in the operating room, allowing control of boththe external and internal surgical environments. The surgeon's interfacehas instrument controllers that can filter tremor and decrease the scaleof motion. Foot pedals expand the surgeon's repertoire, allowing tissuecoagulation and irrigation. Visual feedback is through a proprietarystereoscopic display, called Surgical Immersion™. FDA approval has beenobtained for thoracoscopic, dominal and prostate procedures. Over onehundred DA VINCI® systems have been sold, and have been used to performcholecystectomies, Nissen fundoplications, adrenalectomies,nephrectomies, mitral valve repairs, coronary artery bypass grafting andprostatectomies.

Surgical robots in orthopaedics may be classified as positioning ormachining aids. ROBODOC®, used for hip replacement surgery, is anexample of the latter. Again, they lack the dexterity, MR compatibilityand force sensing needed for neurosurgery. The first-generation ROBODOC®was developed by IBM and the University of California Davis campus. Thesystem was initially tested on 26 dogs in 1990. A second-generationROBODOC® was built by Integrated Surgical Systems, and human trialsconducted. In contrast, Kienzle developed a positioning device for totalknee replacement (TKR). It locates the tibia and femur, and correctlypositions the drill guide for the surgeon. Guide blocks are insertedinto the drill holes, allowing the surgeon to accurately prepare thepatient's bones for joint implantation. A similar system, named theAcrobot, has been developed by the Imperial College group and isdesigned for accurate machining of bone surfaces in TKR surgery. All thesystems mentioned depend on preoperatively placed fiducial markers.Patents on this development are U.S. Pat. Nos. 5,695,500; 5,397,323(both Taylor); U.S. Pat. Nos. 5,086,401 and 5,408,409 (both Glassman)issued in 1992 to 1997.

Robots designed for neurosurgical applications are generally restrictedto positioning and holding instruments for simple procedures such asstereotactic biopsies.

In 1991, Drake reported the use of a PUMA 200 robot as a neurosurgicalretractor in the resection of six thalamic astrocytomas. It is the samemachine that was first used by Kwoh in 1985 to perform stereotacticbiopsies. The robot has revolute joints and has six DOF. Individualjoints are moved by DC servomotors, and their position and velocitytracked by optical encoders. The robot arm could be programmed to moveinto position, or manually manipulated in a passive mode. Itsrepeatability was measured at 0.05 mm, and error of accuracy at 2 mm.Its pneumatic gripper was used to clasp a brain retractor only. Thecases were all performed with a BRW stereotactic frame in place, securedto the same rigid structure as the PUMA arm. This allows for stabletransformation of stereotactic to robotic coordinates. Targetcoordinates were transferred to a computer work station with 3D CTimages, enabling the brain retractor to be accurately placed in relationto the lesion. Progress in developing this system was limited by theinability to rapidly render updated 3D brain images in the operatingroom. The recent convergence of advanced computing, software and iMRimaging now allows us to initiate sophisticated neurorobotics.

A six DOF robot has also been used by Benabid from 1987 to positionbrain cannulae. It is attached to a stereotactic frame, and can usespatially encoded data from Xray, CT, MR imaging and angiography to plotits path. These images are also fused with digitized brain atlases toassist in surgical planning. Hundreds of stereotactic cases have beenperformed, including endoscopy (1-3). Similarly, URS (Universal RoboticSystems) has developed a six DOF hexapod robot called Evolution 1 forbrain and spinal surgery. This system is based on a parallel actuatorconfiguration, which provides it with high positional accuracy and largepayload capacity. The positional accuracy is essential for stereotacticprocedures and the high payload capacity may make Evolution 1particularly well suited for drilling applications such as pedicle screwplacements in the spine.

A simulation tool for neurosurgery, ROBO-SIM, has recently beendeveloped. Patient imaging data is entered and the surgical target andcorridor can be selected and planned. Virtual constraints aredetermined, creating no-go zones. The system can be connected to arobotic arm, NEUROBOT, which holds and positions an endoscope for thesurgeon. NEUROBOT has four degrees of freedom if pivoted around theburr-hole. At this time, there are no published reports of it being usedon patients. It is attached to a stereotactic frame, and can usespatially encoded data from Xray, CT, MR imaging and angiography to plotits path. Again, the systems have only one robotic arm and cannotemulate a human surgeon.

A dextrous robot called the Robot-Assisted Microsurgery system (RAMS),was developed by NASA's Jet Propulsion Laboratory. The mechanicalsubsystem is a six-DOF robot slave arm driven by tendons. This allows alarge work envelope. It is designed to have 10 microns positioningaccuracy. The master input device also has six tendon-driven joints.Simulated force feedback has been used, and it has potential to be usedtele-robotically. RAMS is capable of being used to enhance various typesof microsurgery, including opthalmology. Although RAMS has the requireddexterity, it is still a single arm system lacking the ability toreposition itself over a large worksite. It is also not MR compatibleand has no direct force feedback sensing capability and is notimage-guided. Patents on this development are U.S. Pat. Nos. 5,784,542;5,710,870; 6,385,509 and 6,233,504 all of Das and Ohm et al issued in1998, 2001 and 2002.

The only MR compatible ‘robot’ is a simple experimental system developedby Chinzei and at the Brigham and Women's Hospital in Boston, USA. Therobot consists of a passive instrument holder attached to Cartesiantranslational stages. The limited capabilities of the device caused itto fall into disuse.

The progress of clinical neurological sciences has depended on accuratecerebral localization and imaging technology. Over the past century,advances in cerebral imaging including contrast angiography,pneumoencephalography, and in more recent decades, ultrasound imaging,CT, MRI and frameless stereotactic navigation technology haverevolutionized cerebral localization. Neurosurgery's dependence onimaging technology is epitomized by the recent flurry of iMR imagingsystems developed to provide MR images during a neurosurgical procedure.Since 1996, multiple MR systems and related technologies have beendeveloped, with over 3000 neurosurgical procedures performed worldwide.The systems possess magnet field strengths ranging from 0.12 to 1.5Tesla, associated with varying degrees of intrusion into standardneurosurgical, anaesthetic and nursing procedures and protocols.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is a provided anapparatus for use in surgical procedures comprising:

-   -   a robot for operating on a part of a patient, the robot        including:    -   a movable support assembly arranged to be located in fixed        position adjacent a patient;    -   two movable arms each carried on the support assembly;    -   each arm having redundant degrees of freedom of movement;    -   each arm having an end effector for carrying various surgical        tools (one at a time) for operation on the patient;    -   each end effector including force sensors for detecting forces        applied to the tool by engagement with the part of the patient;    -   a microscope arranged to be located at a position for viewing        the part of the patient;    -   and a workstation and control system including:    -   a pair of hand-controllers, simultaneously manipulated by a        single surgeon, each operable to control movement of a        respective one of the arms;    -   each hand-controller having force feedback arranged to be        controlled in response to the detected forces for providing        haptic feedback to the operator;    -   a first display for displaying at least one image from the        microscope; and    -   a second display for displaying on an image of the part of the        patient the real-time location of the tool.

The device described in more detail hereinafter is a surgeon-operatedrobotic system for neurosurgery that is compatible with a MagneticResonance (MR) imaging system. The system allows a microsurgeon tomanipulate tools tele-robotically from a control room adjacent to theoperating theatre, or at a considerable distance (e.g. intercontinentaland low earth orbit), and works with a specialized set of modified toolsbased on a subset of the standard neurosurgical tool set. The robot andtools provide 16 degrees-of freedom (DOF) movement and consists of twoindependently controlled surgical arms (each with eight DOF) and acamera system to view the work-site. Its function is integrated with amicroscope which is placed behind the robot base, except when the robotis in stereotaxy mode and has moved down the bore of the MRI system.

The arrangement described provides a safe surgical robot that:

-   -   has two robotic manipulators to perform surgical functions with        a precision and dexterity better than the best neurosurgeon;    -   is compact enough to fit and work inside an MRI magnet bore;    -   is completely non-magnetic including all mechanical structures        and actuators and does not interfere with MR imaging;    -   allows a variety of neurosurgical tools to be used;    -   achieves true image-guided surgery by registration of iMRI        fiducials registered by a digitizer on the robot base, and        updating this positional data with information from encoders in        the robot joints. This enhances the surgeon's situational        awareness by constantly updating the position of the tool tips        in relation to the surgical target; and    -   provides the surgeon with a sense of feel in three DOF, that is        it has haptic capability.

The robotic system has two basic modes of operation: microsurgery, andstereotactic surgery. Cranial stereotactic procedures will take placewithin the bore of the magnet. Microsurgical procedures will beperformed outside the magnet and will involve other staff workingco-operatively with the robotic system.

The use of robotics in microsurgery allows for precise motions that canbe guided by microscope and/or MR images obtained during the surgicalprocedure, and represents a significant advance in this field. The robotwill be used for parts of the procedure that require precise, tremorfree motions or geometric accuracy, and as a link between the MR imagesand physical reality.

The system consists of a Neurosurgical Robot, a System Controller and aSurgical Workstation. The physician controls the neurosurgical robot,located in the Operating Room, via a Surgical Workstation located in aseparate Control Room. FIG. 1A is a schematic view of the use of thissystem with an MRI machine. The system architecture is based on a“master-slave” control where the robot arm motions are slaved to thehand-controllers manipulated by the surgeon. To enhance smooth andprecise motion of the surgical tool, tremor filters are incorporated andthe motions of the arm may also be scaled down.

The workstation consists of the Human-Machine Interface (HMI), computerprocessors, and recording devices. The HMI includes two hand controllersthat are used to control the spatial position and actuation of thesurgical tools grasped by each arm. The surgical workstation is equippedwith 4 display panels and one binocular display: one showing the 3D MRimage of the brain and a real-time position of the surgical tool withinthe operating site; a computer status display showing system data of therobotic system; a real-time color view of the operative site captured bya field of view camera system; a 2D high resolution display of theoperative field, and a 3D binocular display of the operative field. Bothof the microscope displays are interfaced with high resolution camerasmounted on the right and left ocular channels of a standard surgicalmicroscope. An additional display provides system data and controlsettings. The workstation contains recording devices to storeintra-operative MRI and video imagery and system data. An electricalcable harness connects the robot to the System Controller. Thecontroller translates the workstation and hand-controller commands intoinputs for the robotic arm motor drives and sensors. The SystemController contains the servo-control electronics that independentlymove and position the robot arms. The System Controller also includes aninterface for the optical joint encoders and thermistors. The backboneof the System Controller is an elaborate array of software modules andelectrical hardware. The architecture of the System Controller isdesigned to enhance safety by single fault tolerant software andredundant electrical back-up.

The robot consists of two articulated arms with dexterous mechanicalmanipulators that grasp and move surgical tools attached to the armend-effectors.

For precise tool positioning, each of the surgical arms has eight DOF.The arms are each independently small enough to operate within theconfines of the working diameter of the IMRIS closed bore magnet and thedevice can be operated to select one or the other arm. Both can worksimultaneously within an open magnet of either vertical or horizontaldesign. They provide frame-less stereotactic functionality whenregistered to fiducial markers on the head or spine. Such fiducialmarkers may comprise a component which can be mounted on the patient anddefine artifacts which can be viewed in the MR image. Such MR viewableobjects are usually spherical and are made from an MR responsivematerial which thus generates a readily visible artifact on the MRimage. Other types of optical and MR responsive objects can be used.These targets are localized and registered using a robot base-mountedmechanical digitizing arm. The images defined by the MR system can beregistered relative to the arms of the robot allowing the surgeon toplace the tools at the required location as determined by the MRanalysis.

The robot is mounted on a vertically adjustable mobile base, moved intoposition for the surgical procedure, and mechanically secured usinglocking wheels. The robot can be positioned to function as an assistantor the primary surgeon. The mobile base enables the robot to beintegrated into any operative environment equipped with the appropriateelectronic and mechanical interfaces.

Surgical tools are manually inserted into the arm end-effectors. Thelocation and orientation of the tool tip relative to the surgical targetwill have an accuracy of approximately one-millimeter when relying onframeless navigation alone. Further refinement of toll tip placement isbased on the surgeon assessing the stereoscopic, magnified field of viewprovided by the binoculars at the workstation. The final accuracyachieved is therefore only limited by the combination of the spatialresolution of our visual system (rods and cones) with 30 micronresolution that our robot has achieved on breadboard testing. Thelocation of the tool tip can be continuously monitored using theinternal arm joint angles and the virtual display of the tool acquiredfrom iMRI.

The robot and field camera are designed to be compatible with the MRenvironment. Compatibility ensures that the robot produces minimal MRIartifact and conversely, the operation of the robot is not disturbed bythe strong electromagnetic fields generated by the MR system. Allequipment exposed to the MR field uses compatible materials, componentsand design practices such as:

The robot drive mechanisms use an Ultrasonic piezo-electric actuatortechnology.

The arms and surgical tools are made of MR-compatible materials.

All electronics are RF and magnetically shielded.

Optical force sensors/strain gauges are attached to the tool interfacesto provide force-feedback inputs. The sensors are MR compatible, immuneto electromagnetic interference and possess high sensitivity and fastmeasurement update rates.

The workstation controls the arms by transforming commands from the handcontrollers and transmitting them to the Main Controller. The handcontrollers act as virtual tools for the surgeon. The motion commandsare filtered to remove hand tremor and typically scaled down so, forexample, a 10 cm displacement of the controller would result in a tooltip displacement of 5 mm. As a safety measure, the arms are onlyactivated if a hand switch is depressed. This will avoid inadvertentmovement of the arms caused by an accidental bumping of the handcontroller. In addition to providing commands to the robot, theworkstation receives feedback from the robot, the Main Controller, theMR system and other devices.

The workstation has three display types: Video, MRI and Control. Thevideo recordings of the surgical worksite are taken by stereo camerasmounted on the surgical microscope and displayed on a high resolution 2Ddisplay and a 3D binocular display, providing the surgeon with a senseof depth. A third video display is used to show a video image of theoperating room. The MRI display shows the patient's imaging data with avirtual tool position superimposed on the image. This enables thesurgeon to view and track the tool in real-time, thereby facilitatingimage-guided surgery. The MRI can be enhanced by the administration ofintravenous contrast agents to show the lesion and its relationship toadjacent structures. Lastly, the Control display is used to monitor thecontrol systems of the robot.

Surgical simulation software on the workstation allows the surgeon toplan the point of cranial trepanation and calculate safe trajectoriesfor the surgical corridor. Virtual ‘no-go’ boundaries can be defined bythe surgeon, preventing inadvertent injury to neural elements. Theprocedure can be practiced in virtual mode by the surgeon. This will beparticularly useful when performing a rare procedure, as well as inhelping to teach trainee neurosurgeons.

The following sections outline the systems, electromechanical, andworkstation components and specifications.

System Description

The workstation consists of the crucial Human-Machine Interface (HMI),computer processors, and recording devices. The HMI includes twohand-controllers used to control the motion and position of the surgicaltools grasped by each arm. The surgeon has multiple surgical displays:one showing the 3D MR image of the brain and a real-time position of thesurgical tool within the operating site, and the other a real-time colorview of the surgical site captured by the surgical microscope. A thirddisplay will provide system data and control settings. The workstationcontains recording devices to store intra-operative video imagery andsystem data. An electrical cable harness connects the robot to the MainController. The controller translates the workstation andhand-controller commands into inputs for the robotic arm motor drives.The Main Controller contains the servo-control electronics thatindependently move and position the robot arms. The Main Controller alsoincludes an interface for the optical joint encoders and thermistors.The backbone of the Main Controller is an elaborate array of softwaremodules and electrical hardware. The architecture of the Main Controlleris designed to enhance safety by single fault tolerant software andredundant electrical back-up.

Electro-Mechanical Components

The robot is configured as a yaw plane manipulator to reduce the numberof joints affected by gravity. It consists of two articulated arms withdexterous mechanical manipulators that grasp and move surgical toolsattached to the arm end-effectors. A vision system consisting of an MRcompatible camera system and white LED lights is mounted on the base andmanually adjusted.

For precise tool positioning, the surgical arms have 8-DOF per arm(including tool actuation). The arms are small enough to individuallyoperate within the confines of the 68-cm working diameter of the 1.5 Tmagnet. The robot is mounted on a mobile base, moved into position forthe surgical procedure, and mechanically secured using wheel brakes. Therobot can be positioned to function as an assistant or the primarysurgeon. The mobile base enables the robot to be integrated into anyoperative environment equipped with the appropriate electronic andmechanical interfaces.

Surgical tools are manually inserted in the arm end-effectors. Formicrosurgical procedures, standard tools such as forceps, needledrivers, suction, micro-scissors and dissectors are created to fit theend-effectors. The tool actuation mechanism is comprised of a mobilering surrounding the tool handle, the vertical movement of whichcontrols tool actuation. Circular movement of a gear mechanism generatestool rotation. Based on the end-effector configuration, a novelmicro-scissor design was implemented. For stereotactic procedures, alinear drive mechanism was designed to provide accurate insertion andtargeting of a cannula and introducer. Each tool is equipped with anidentifier bar and color code to automatically configure software 3Dmodels. The models are used to calculate the location and orientation ofthe tool tip relative to the surgical target to an accuracy ofone-millimeter. This absolute accuracy is limited by the resolution ofinputs from the spatially encoded MR data and also the registrationmethod. The registration method involves calibrating the robotcoordinate frame to the MR image of the patient using MR fiducials andmechanical digitizing points. The location of the tool tip iscontinuously monitored using a kinematic model combined with internalarm joint angles and the virtual display of the tool acquired from iMRIor other imaging modalities such as 3D ultrasound. The tool position iscalibrated mechanically and checked against its position determined fromupdated MR images. An incremental tool tip resolution of 30 microns canbe obtained.

The robot and field of view camera are designed to be compatible withthe MR environment. Compatibility ensures the robot produces minimal MRIartifact and conversely, the operation of the robot is not disturbed bythe strong electromagnetic fields generated by the MR system. Allequipment exposed to the MR field utilizes compatible materials andcomponents including:

Piezoelectric motors are used for the robot drive mechanisms. They havethe advantage of being non-magnetic, self-braking, MR-compatible, andable to meet the operating time specifications.

Material selection is critical for robot stiffness and MR compatibility.The upper and lower arm structural components are made of titanium andPEEK (Polyetheretherketone) respectively. Both materials have a veryhigh resistivity, permitting placement inside the RF coil duringtransmission with minimal degradation of the coil quality factor. Theintra-operative magnet and RF coil can accommodate titanium and PEEK inthe imaging volume without significant loss of performance.

All electronics are RF and magnetically shielded and located as far fromthe high intensity fields as practical.

A three DOF optical force sensor system is used to provide hapticfeedback to the surgeon. The design is based on the photo-elastic effectto measure strains in materials under stress. The end-effector isequipped with deformable flexures providing an interface for thesurgical tools. Each flexure is positioned mutually perpendicular andcontains its own optical strain sensor. This arrangement allows strainsto be measured at the flexure surfaces. These strain measurements areused to calculate tool tip forces in the X, Y, Z directions, which arethen sent back to the workstation hand controllers.

Surgical Workstation

The Surgical Workstation incorporates a computer processor, twohand-controllers to manipulate the robot arms, a controller forpositioning the microscope and lights, three types of display, and datarecorders. The interface is designed to maximize ergonomic comfort andminimize surgeon fatigue.

In addition to providing commands to the robot, the workstation receivesfeedback from the robot, the Main Controller, the MR system, and otherdevices. The type of information received includes: Video from thestereo camera viewing the surgical work site via the microscope;preoperative and iMR image data; tool position and motion data from therobot controller; force-sensing (haptic) data from each arm; diagnosticor error messages from the robot controller; simultaneous talk/listenvoice communication with operative staff; and patient physiologic data.

Hand-Controllers

The workstation controls the arms by transforming commands from thehand-controllers and transmitting them to the Main Controller. Thehand-controllers act as virtual tools for the surgeon and have6-Degrees-of-Freedom (DOF) with 3-DOF positional force feedback. Thesystem has a large workspace and high force feedback fidelity. Motioncommands are filtered to remove hand tremor and typically scaled down.For example, a 10-cm displacement of the controller could result in atool tip displacement of 5 mm. As a safety measure, the arms are onlyactivated if a hand switch is depressed. This avoids inadvertentmovement of the arms caused by an accidental bumping of thehand-controller. The user interface of the hand-controller has beendesigned to maximize ergonomic comfort.

Visual Displays/Optics

The Video display presents a 3D stereoscopic view of the surgical siteproviding the surgeon with a sense of depth. Two precision aligned videocameras are fitted to the right and left ocular channels of a standardsurgical microscope. Camera signals are presented on a proprietaryhigh-resolution virtual stereomicroscope (binoculars) at theworkstation. The same camera signal is displayed on a 2D—HDTV (HighDefinition Television) screen. The HDTV is positioned above thebinoculars and serves as an alternative visual display for the surgeonand as a primary display for surgical staff and students. The binoculardisplay was chosen over conventional 3D stereoscopic displays withpolarization glasses to minimize the effects of ghosting and also toincrease contrast and color depth of the image. The microscope isequipped with a support stand capable of motorized tilt of themicroscope head. These mechanized features of the microscope allow thesurgeon to remotely adjust the microscope head from the SurgicalWorkstation. Magnification and working distance can be controlled fromthe Workstation.

The MRI display shows a virtual tool position superimposed on theimages. This enables the surgeon to view and track the tool inreal-time, thereby facilitating image-guided surgery. The MRI isenhanced to show the lesion and its relationship to adjacent structuresin both 2- and 3-dimensions.

The Control Panel display will show the following data:

-   -   System configuration: operational modes, calibration,        hand-controller parameters    -   Robot status: tool angles and depth, system status messages,        force sensor data    -   Physiological data: heart rate, blood pressure, expired pCO2,        urinary output, blood loss, oxygen saturation    -   Operational scripts to outline the step-by-step procedures and        contingencies

Image Guidance, Simulation, and Registration

The image guidance system of robot provides the surgeon a means ofnavigation, target localization and collision avoidance. Surgicalsimulation software on the workstation allows the surgeon to plan thepoint of cranial trepanation and calculate safe trajectories for thesurgical corridor. Virtual boundaries defined by the surgeon preventinadvertent injury to neural elements. Simulated procedures can bepracticed in virtual mode by the surgeon.

Registration of the robot is performed using a pre-operative MRI scanand MR fiducial targets that remain near the surgical field throughoutthe operation. The registration between the robot and the fiducials isaccomplished using a compact 3-D digital coordinate measurement arm(digitizer) located on the base of the robot. The surgical assistantuses the digitizer arm to measure the coordinates of touch points onregistration targets located near the surgical field. The coordinatesare transmitted to the workstation, which uses the data to calculate thegeometric coordinate transformation.

Safety Challenges and Solutions

It is a purely passive device and is exclusively controlled by anexperienced surgeon at the workstation. An additional surgeon will alsobe scrubbed for microsurgical cases and will be able to manuallyintervene if ever needed. Audio communication between the robot operatorand the OR team will be provided, and a video display of the worksiteand MRI display duplicated in the OR. The robot's work envelope istailored to a specific procedure, and suitably restricted. In additionto this, no-go zones are programmed into the proposed operation duringthe surgical planning phase. The software controlling the robot insistson continuous input from the surgeon, and a dead-man switch (safetyinterlock) also requires ongoing activation to prevent a lockdown. Auser selectable limit is set via the software that will limit the amountof force that can be applied and can be affected by a current limit setat the servo level. If actuators fail, intrinsic braking willautomatically freeze the robot. The actuators themselves are designed tofunction at low torque and force levels, reducing the risk of tissueinjury. This has the added benefit of using small, light motors thatenhance robot balance and dexterity. End-effector/tool motion will alsobe considerably slowed down when operating within a microsurgicalcorridor. It can perform dissection at a pace of 1 mm/sec or beaccelerated to as much as 200 mm/sec when outside the work envelope andreaching out for tool changes. The transition to faster speeds willrequire two sequential but different electronic commands to preventaccidental speeding. The mobile iMRI also has inbuilt braking systemsand moves at slow speeds as it approaches patients. Unplanned powerinterruption results in ‘default’ freezing of movements, and personnelcan deliberately cut power through strategically placed emergency stop(E-Stop) buttons.

Clinical curbs also minimize patient risk. The current robot is excludedfrom performing skull exposure, as this would be a relatively difficulttask for a robot but is efficiently accomplished by a surgeon.Similarly, burr-holes and bone-flaps are executed by surgeons.

The system provides an MR-compatible ambidextrous robotic system capableof microsurgery and stereotaxy. With additional surgical toolsets thissystem lends itself to other disciplines including plastic,opthalmological and ENT surgery. The system has a uni-dexterousconfiguration for deployment within a magnet bore allowing updated imageguidance for stereotactic procedures. This configuration providesadditional range of motion within the magnet bore. Complex microsurgery,where both robotic arms are employed, is performed outside the magnetunder supervision of a scrubbed surgeon. This will also facilitatesafety and tool changing.

The system has been created de novo for the specific purpose ofperforming microsurgery and stereotaxy. This includes standardtechniques such as micro-dissection, thermo-coagulation, and finesuturing. Procedures such as tumor resection and aneurysm clipping arepossible. The design of the robot is inclusive and versatile however,and is ideal in other microsurgical specialties such as opthalmology.The fine dexterity and low payload of the end-effectors precludes theiruse in gross manipulation of tissue and bone, as these tasks are morereadily suited to humans. Other unique features includeMRI-compatibility as tested at 3 T, and a mechanical navigation system.This makes the system the first truly image-guided surgical robot. It isalso the only surgical robot with eight-DOF per arm (including toolactuation). Although this is significantly less than human DOF, itexceeds the six-DOF required to position a tool precisely in space andthen orient it in the desired plane. Unnecessary DOF result incumulative instability while insufficient DOF result in limitedpositioning of the manipulator. Surgeons performing microsurgery willinstinctively eliminate redundant DOF by fixing their shoulder and elbowjoints, but retain adequate dexterity in the hands and wrists to performdelicate microsurgery. The manipulators were designed to have thenecessary dexterity to perform these same tasks.

The system provides the first authentic force feedback system insurgery. Coupled with an exceptional visual system, based on militaryoptics, and auditory feedback from the surgical site, the systemrecreates the sound, sight and feel of conventional neurosurgery. Thehaptic sensibility component will also be useful for simulating rareprocedures, and teaching neurosurgical residents.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be described in conjunction withthe accompanying drawings in which:

FIG. 1A is a schematic view of a neurosurgeon, surgical workstation,main controller, and MRI processor and controller located in a surgicalcontrol room while the robot (labeled “Neurobot” in the figure), the MRImagnet and the patient are located in an operating room.

FIG. 1B is a schematic overview of the system according to the presentinvention.

FIG. 2 is an isometric view from the rear and one side of the robot ofthe system according to the present invention.

FIG. 3 is an isometric view of the robot of FIG. 2 from the front andopposite side.

FIG. 4 is an isometric view of the workstation of the system of FIG. 1B.

FIG. 5 is a schematic illustration of the operation of the pivots of thearms of the robot of FIG. 2.

FIG. 5A is a cross-sectional view of one of the pivots of the arms ofthe robot of FIG. 2.

FIGS. 6 and 7 are isometric views of one arm of the robot of FIG. 2.

FIG. 8 is a top plan view of the robot of FIG. 1B showing one armadvanced for insertion into a magnet bore of an MRI imaging system andthe other arm retracted to allow engagement of the cabinet with thebore.

FIG. 9 is a side elevational view of the robot in the configuration ofFIG. 8.

FIG. 10A shows schematic side, top, front and back views of the robotused with an open bore MRI magnet.

FIG. 10B is side elevational view of the robot in the configuration ofFIG. 8 in conjunction with a patient table and the MRI magnet.

FIG. 11 is an end elevational view of a patient operating table andincluding the robot in co-operation with the microscope and locationregistration system.

FIG. 12 is an enlarged side elevational view of the end effectorincluding a pair of forceps mounted in the end effector.

FIG. 13 is an enlarged isometric view of the end effector of FIG. 12.

FIGS. 14, 15, 16 and 17 are isometric views of the main components ofthe end effector of FIG. 12 including four different tools, specificallya suction tool, a micro-dissection tool, micro-scissors and bipolarforceps respectively.

DETAILED DESCRIPTION

Further details of the above generally described system are shown in theattached drawings 1 through 17.

An overview of the system is shown in FIG. 1B which comprises a robotmanipulator 10, a work station 11 and a controller 12 which communicatesbetween the robot manipulator and the work station. As inputs to thework station is also provided a stereo microscope 13, an MRI imagingsystem 14 and a registration system 15.

The work station includes a number of displays including a first display16 for the MRI image, a second display 17 for the microscope image and athird display 18 for the system status. Further the work stationincludes two hand controllers schematically indicated at 19 and an inputinterface 20 allowing the surgeon to control the systems from the workstation while reviewing the displays. The work station further includesa computer or processor 21, a data recording system 22 and a powersupply 23.

The display 17 includes a stereoscopic display 17A which provides asimulated microscope for viewing the images generated by thestereo-microscope system 13. Further the display 17 includes a monitor17B which displays a two dimensional screen image from the microscopesystem 13.

The robot manipulator 10 includes a field camera 24 which provides animage on a monitor 25 at the work station.

Turning to FIG. 4, a typical layout of the work station is illustratedwhich comprises a desk 126 on which is mounted four monitor screens 16,17B, 18 and 25 together with a microscope viewing system 17A, all ofwhich are arranged to be accessed by the surgeon seated at the desk. Infront of the desk is provided the hand controllers 19 and the inputterminal 20.

The stereo microscope system is of a type which is commerciallyavailable and can be mounted on a suitable support adjacent the patientfor viewing the necessary site. The stereo microscope includes twoseparate imaging systems one for each channel which are transmittedthrough suitable connection to the display 17 at the work station. Thusthe surgeon can view through the microscope display 17A the threedimensional image in the form of a conventional microscope and can inaddition see a two dimensional image displayed on the monitor 17B.

Similarly the magnetic resonance imaging system 14 is of a conventionalconstruction and systems are available from a number of manufacturers.The systems are of course highly complicated and include their owncontrol systems which are not part of the present invention so that thepresent workstation requires only the display of the image on themonitor 16 where that image is correlated to the position of the tool asdescribed hereinafter.

The hand controllers 19 are also of a commercially availableconstruction available from a number of different sources and comprise 6degrees of freedom movable arms which can be carefully manipulated bythe surgeon including end shafts 19A which can be rotated by the surgeonto simulate the rotation of the tool as described hereinafter. Anactuator switch 19B on the tool allows the surgeon to operate theactuation of the tool on the robot as described hereinafter.

The robot manipulator shown in general in FIG. 1B and shown in moredetail in FIGS. 2 and 3 comprises a cabinet 101 and two arms 102 and 103which are mounted on the cabinet together with the field camera 24 whichis also located on the cabinet. The field camera is mounted at the backof the cabinet viewing past the arms of the front of the cabinet towardthe patient and the site of operation to give a general overview fieldof the situation for viewing on the display 25.

In FIG. 1B is also shown schematically the control system forcommunication between the work station and the robot manipulator and forcontrolling the operation of each of those components. The controllerincludes a force sensor sub system 121 and a motion control sub system122 together with power supplies and further components as indicatedschematically at 123. The force sensor sub system controls the feed backforces as detected at the end effector of the robot arm and describes inmore detail hereinafter to the hand control systems 19. The motioncontrol subsystem 122 converts the motion control sensors from thehand-control system 19 into individual operating instructions to thevarious components of the arms as described in more detail hereinafter.The motion control sub system also provides an output which iscommunicated to the work station for display on the MRI imaging monitor16 of the location of the tip of the tool relative to the imagedisplayed on the screen 16, as generated by the registration system 15as described hereinafter.

As shown in FIGS. 2 and 3, the cabinet 101 includes a communicationscable 104 which connects to the controller 12. The cabinet is a mobileunit mounted on castor wheels 105 which allow the cabinet to be moved byhandles 106 manually to a required location. Handles 107 act as brakeswhich lock the wheel and castor rotation so as to locate the cabinet 101at a required position and maintain it fixed. The cabinet containssuitable ballast so that it is sufficiently heavy to prevent any tiltingor toppling or other unintentional movements when the brakes are lockedby the handles 107. The cabinet further includes a top section 108 whichcan be raised and lowered by a manually operable handle 109 so as toraise and lower a top mounting surface 110 which supports base plates111 of the arms 102 and 103. Thus an operator can wheel the cabinet tothe required location and can raise and lower the arms to a pre selectedheight so as to register with a required location for the site of theoperation whether that be microsurgery on an operating table orstereotactic procedures within the bore of a magnet. The field camera 24is mounted on a stanchion 241 so as to stand upwardly from the topportion 110 and to view forwardly across the arms 102 and 103 to thepatient and the site.

For convenience of illustration, the structure of the arms is shownschematically in FIG. 5, where the arms are mounted with their base 111attached to the top surface 110 and shown schematically. Each of thearms 102 and 103 includes a number of joints as shown and describedhereinafter which allow operation of a tool schematically indicated at26. Thus each arm includes a first joint defining a shoulder yaw pivot131 defining a vertical axis of rotation. On the vertical axis ismounted a second joint 132 forming a shoulder roll joint which providesrotation around a horizontal axis 133. The shoulder yaw axis 134 extendsthrough the joint 132. A rigid link 135 extends from the joint 132 to anelbow joint 136 which is cantilevered from the shoulder roll joint 132.The elbow joint includes an elbow yaw joint 137 and an elbow roll joint138. The yaw joint 137 is connected to the outer end of the link 135 andprovides rotation about a vertical axis 139. The roll joint 138 islocated on the axis 139 and provides a horizontal axis 140 A link 141lies on the horizontal axis 140 and extends outwardly from the joint 138to a wrist joint generally indicated at 142. The wrist joint 142includes a wrist yaw joint 143 and wrist pitch joint 144. The wrist yawjoint 143 is located at the outer end of the link 141 and lies on theaxis 140. The wrist yaw joint provides a vertical axis 145 about which alink 146 can pivot which carries the pitch joint 144. The pitch joint144 provides a horizontal axis 147 which allows the tool 26 to rotatearound that horizontal axis 147. The tool 26 includes a roll joint 148which provides rotation of the tool 26 around its longitudinal axis. Thetool further includes a tool actuator 149 which can move longitudinallyalong the tool to provide actuation of the tool as described in moredetail hereinafter.

It will be noted that the axes 134, 139 and 145 are all vertical so thatthe weight of the supported components has no effect on the joint andthere is no requirement for power input to maintain the position of thesupported component to counteract its weight.

With regard to the horizontal joint 147, there is nominally a componentof the weight of the tool which is applied to cause rotation around theaxis 147. However the tool is located close to the axis 147 so thatthere is little turning moment around the axis 147 resulting in verylittle weight is applied onto joint 144. Thus the weight component to berotated around the axis 147 is minimized thus minimizing the amount offorce necessary to counteract the weight.

With regard to the axis 140 and the joint 138, it will be noted that thetool and the links 141 and 146 are arranged so that the center ofgravity is approximately on the axis 140 thus ensuring the requirementto counteract the weight of those components since those componentsprovide minimum moment around the axis 140.

With regard to the joint 132 and the axis 133, the weight applied to thejoint 132 from the link 135 depends upon the position of the joint 137.Thus if the link 141 is aligned with the link 135 then the center ofgravity of the cantilevered components from the joint 132 liesubstantially on the axis 133 thus minimizing the moment around the axis133. However it is necessary of course to operate the system that thejoint 137 turn the link 141 around the axis 139 thus providing acantilever effect to one side of the axis 133. However again this momentaround the axis 133 is minimized by the selection of the system so thatthe arm normally operates with the center gravity of the portion of thearm outboard of the link 135 minimized.

Thus the forces required to provide rotation around the various axes isminimized and the forces required to maintain the position whenstationary against gravity is minimized.

This minimization of the forces on the system allows the use of MRIcompatible motors to drive rotation of one joint component relative tothe other around the respective axes.

The arrangement described above allows the use of piezoelectric motorsto drive the joints. Such piezoelectric motors are commerciallyavailable and utilize the reciprocation effect generated by apiezoelectric crystal to rotate by a ratchet effect a drive disc whichis connected by gear coupling to the components of the joint to effectthe necessary relative rotation.

An open view of a typical joint is shown in FIG. 5A and includes two ofthe piezoelectric motors P driving a drive plate 501 mounted on a driveshaft 502 carried on the back plate of the housing 503 and in bearingson the front plate (not shown) of the housing. The shaft 502 drives agear which is in mesh with a driven gear 506 on a driven shaft 507. Thedriven shaft 507 rotates one part of the joint relative to the otherpart which is attached to the housing 503 about the joint axis 509.

The joint shown in FIG. 5A uses a dual piezoelectric motor arrangementand is thus used for the larger joints at the shoulder and elbow. Forthe smaller joints such as the wrist and tool actuation, the samepiezoelectric motor is used but one of these motors is used to providethe necessary torque.

A suitable construction of the motors and links for the arms to embodythe schematic arrangements shown in FIG. 5 is shown in FIGS. 6 and 7.Thus the various components are marked with the same reference numeralsas set forth in FIG. 5. It will be noted that the joints are of asimilar construction with each including a piezoelectric motor P mountedin a housing H. The motor P drives the joint by a gear couplingarrangement from a disc at the motor P to the rotatable portion of thejoint on the respective rotation axis. Thus the axis of the motor P isoffset to one side of the axis of rotation of the respective joint andprovides the required controlled rotation determined by the rotation ofthe drive disc of the piezoelectric motor. Dual optical encoders shownas 137 are used at each joint to measure joint angle position. The dualarrangement provides redundancy. The encoder is used to determinewhether the required movement has been obtained.

Turning now to FIGS. 8 and 9, it will be noted that the construction hasbeen operated to move the arms from the double arm operating system to asingle arm operating system for use in co-operation with the bore of aclosed bore magnet. Thus in FIGS. 8 and 9, an additional table portion112 is mounted on the front of the cabinet 101 on mounting pins 113.This allows a selected one of the arms 102 and 103 to be moved with itsbase plate 111 sliding along a track on the table top 112 to a positionadvanced in front of a front wall 115 of the base cabinet 101. At thesame time the other of the arms is turned to a retracted position sothat it is wholly behind the front wall 115 as best shown in FIG. 8.Either of the arms can be selected for movement in a respective track tothe forward position since the arms have different work envelopes withinwhich they can move so that, depending upon the location of the site inwhich operation is to take place, one or other of the arms provides abetter field of operation and thus should be selected. The remaining armremains in place on the table top 110 and is suitable retracted to avoidinterference with the opening of the magnet bore.

The robot therefore can be used in the two arm arrangement formicrosurgery in an unrestricted area outside of the closed bore magnetor for microsurgery within an open bore of a magnet should thearrangement of the magnet be suitable to provide the field of operationnecessary for the two arms to operate. The two arms therefore can beused with separate tools to affect surgical procedures as describedabove. Such an arrangement in shown in FIG. 10A.

Within the bore of a closed magnet, there is insufficient room toreceive both arms of the device so that the single arm can be used toeffect stereotactic procedures. Such procedures include the insertion ofa probe or cannula into a required location within the brain of thepatient using the real time magnetic resonance images to direct thelocation and direction of the tool. Thus the single arm system can beused to carry out whatever procedures are possible with the single armbut procedures requiring two arms must be carried out by removing thepatient from the closed bore moving the patient to a required locationwhere sufficient field of operation is available, restoring the robot toits two arm configuration with the table top 112 removed and locatingthe robot at the required position relative to the patient and theoperating table.

In FIG. 10B, the system is shown schematically in operation within thebore of a magnet 30 of the MRI system 14. The bore 31 is relativelysmall allowing a commercially available patient table 32 to carry therequired portion of the patient into the bore to the required locationwithin the bore. The field camera is used within the bore for observingthe operation of the robot 10 and particularly the tool 26.

The registration system 15 (see FIG. 11) includes a mount 35 fixed tothe head of the patient and including fiducial markers 36 carried on themount. The mount is of a conventional head clamp constructioncommercially available. The fiducial markers are small objects which arelocated at fixed positions around the head of the patient in apredetermined configuration or array which can be located by theregistration system so as to properly orient the registration systemrelative to the image generated by the MRI system 14. Thus the fiducialmarkers are formed of a material which is visible on the MR image sothat the markers can be seen in the image as displayed on the monitor16.

The same fiducial markers can be used in the MRI system even when therobot is not used in the MRI system for carrying out any procedures sothat the image generated on the MRI system is registered relative to thefiducial markers or points located on the head of the patient.

As shown in FIG. 11, the patient on the table 32 is moved to theoperating position which is accessible by the arms 102 and 103 and thetools 26 carried thereby. The patient carries the head restraint 35which is fixed in the same position relative to the head of the patientas it was during the MRI process including the fiducial markers 36.

At the operating position on the table 32 is located the microscope 33on the stand 34 which is moved to position the microscope to view theoperating site at the operating location on the table 32.

The registration system 15 includes a stand 37 carrying a registrationprobe and associated control system 38 with the probe including a probetip 39. The registration system 38 is mounted at a fixed position sothat the location of the probe tip 39 in X, Y and Z coordinates can belocated and determined by the registration system for communication tothe controller 12.

Thus, with the patient fixed in place by the clamp 35, the position ofeach of the fiducial markers 36 is identified by the tip 39 thusproviding to the system the co-ordinates of that fiducial marker. Inaddition the instantaneous position of the tip of the tool 26 is inputinto the same system thus registering the tool tip relative to thefiducial markers and therefore relative to the image displayed on themonitor 16.

The system is therefore operated so that the controller 12 operates tomove the tool tip to a required position and at the same time indicatesto the display system the actual location of the tool tip in theregistered space defined by the fiducial markers and displayed on themonitor 16. The surgeon is therefore able to view the location of thetool tip on the monitor 16 relative to the previously obtained image andmaintain the registration of those images.

In procedures carried out during the MR imaging process, the tool tipcan be formed in manner which allows it to be visible in the image sothat the surgeon obtains a real time image from the MRI system whichlocates the tool tip relative to the volume of interest visible on themonitor displaying the image.

The end effector is shown in FIGS. 12 through 17. The tool 26 is mountedon its upper end in the role actuator 148 so as to extend downwardlytherefrom to the tip 40. The upper end of the tool is supported whileallowing some side to side and front to back movement of the toolrelative to the actuator 148. This movement is constrained by a collarat the actuator 149 which surrounds the tool and holds the tool alongthe axis of the actuator 148.

The tool support mechanism 148 allows rotation about the longitudinalaxis 42 of the tool by a drive gear 150 actuated by a further motor P.Thus the tool, while held on the axis 42 can be rotated around itslength to move the tip 40 of the tool around the axis.

Actuation of the tool is effected by moving the actuator 149longitudinally of the axis 42. For this purpose the actuator 149 ismounted on a slide 43 carried in a track 44 and driven by a suitablemechanism along the track 44 so as to accurately locate the position ofthe actuator 149 along the length of the tool.

In the example shown in FIGS. 12 and 13, the tool comprises forceps 45which are actuated by moving the ring 46 of the actuator 149 along rampsurfaces 47 on the sides of the blades of the forceps 45. Thus theposition axially of the ring 46 along the ramp surfaces 47 determinesthe spacing of the tips of the forceps.

Detection of the forces is applied on the tip 40 by an object engaged bythe tip 40 is effected by top and bottom flexure detection components 52and 53. Thus the actuator 148 is mounted on the top flexure componentwhich is arranged to detect forces along the axis 42. The bottom flexurecomponent is attached to the actuator 149 and is used to detect side toside and front to back forces in the X, Y plane.

Suitable flexure detection components are commercially available anddifferent types can be used. For use in the magnet, however, thedetection components must be MRI compatible.

One suitable example of a flexure detection system is that which uses aknown optical detection system. Thus the flexure component includes amember which is flexed in response to the forces and the flexure ofwhich changes the characteristics of reflected light within the member.Fiber optic cables supply a light source and receive the light componentfrom the reflection, communicating the reflected light through the armto a control module within the cabinet of the robot. Thus forces flexingthe member in response to engagement of the tip of the tool with anobject are communicated to the control module within the cabinet whichconverts the reflected light to an electrical signal proportional to theforces applied.

The control module in the cabinet communicates the electrical signalsproportional to the forces to the controller 12 of the system. Theseforces are then amplified using conventional amplification systems andapplied to the hand controllers so as to provide the previouslydescribed haptic effect to the surgeon at the hand controllers.

In FIG. 14 is shown a suction tool 55 which is used in replacement forthe forceps shown in FIG. 13. Thus the forceps are removed by slidingthe tool 26 longitudinally out of its engagement with the upper rollactuator 148. Thus the tool is removed from the ring 46 of the loweractuator 149. The suction tool 55 includes a connection 56 to a sourceof suction for applying a suction effect at the tip 40 of the suctiontool. The amount of suction applied at the tip 40 relative to thesuction source is controlled by moving the actuator ring 46longitudinally of the tube 57 forming the tool. The tube 57 includes aninlet opening at the ring 46 which is partially or wholly covered by thering 46. Thus when the opening 58 is fully exposed as shown in FIG. 14,the suction effect is minimized or removed so that little or no suctionis applied at the tip 40. Partial covering of the hole 58 increases thesuction effect up to a maximum when the hole is fully covered by thering 46.

In FIG. 15 is shown a micro dissection tool 61 which is mounted aspreviously described. This tool simply comprises an elongated tool bar59 with a tip 60 shaped for various well known functions which areavailable to the micro surgeon. As previously described, the tip can berotated to a required orientation around the axis of the tool bar. Inthis tool, the lower actuator 149 is not operated but is merely used todetect side to side and front to rear forces as previously described.

In FIG. 16 is shown a micro scissors tool 62 which is mounted in theupper and lower actuators as previously described. The scissors includea tool bar which is held at its upper end 64 by the upper actuator,together with an actuator rod 65 which is carried by the lower actuator149. Upward and downward movement of the rod 65 actuates one blade 66 ofa pair of scissors blades 66 and 67 in a cutting action by pivoting theblade 66 about a suitable support pivot 68.

1. A method of operating a surgical system, comprising: obtaining amagnetic resonance imaging (MRI) scan in which magnetic resonance (MR)visible targets are located; registering positional data for a roboticarm to the MRI scan using a digitizing tool, the robotic arm configuredas a yaw plane manipulator and including: multiple joints and multipledegrees of freedom, the multiple joints including a first yaw joint, asecond yaw joint and a third yaw joint, the yaw joints operativelylinked by a plurality of roll joints; an MR-compatible structuralmaterial; multiple MR-compatible joint motors; multiple MR-compatiblejoint encoders; and an end effector holding an MR-compatible surgicaltool having a tool tip; and displaying a location of at least the tooltip relative to an image from the MRI scan.
 2. The method of claim 1,where the robotic arm has six degrees of freedom.
 3. The method of claim1, further comprising: driving the MR-compatible joint motors based oninput from an operator that is filtered to remove hand tremor.
 4. Themethod of claim 1, further comprising: driving the MR-compatible jointmotors based on input from an operator that is scaled.
 5. The method ofclaim 1, further comprising: driving the MR-compatible joint motorsbased on input from an operator that is scaled and that is filtered toremove hand tremor.
 6. The method of claim 1, where the registeringfurther comprises: registering positional data for a second robotic armto the MRI scan using a digitizing tool, the second robotic armconfigured as a yaw plane manipulator and including: multiple joints andmultiple degrees of freedom, the multiple joints of the second roboticarm including a first yaw joint, a second yaw joint and a third yawjoint, the yaw joints of the second robotic arm operatively linked by aplurality of roll joints; an MR-compatible structural material; multipleMR-compatible joint motors; multiple MR-compatible joint encoders; and asecond end effector holding a second MR-compatible surgical tool havinga tool tip.
 7. The method of claim 1, further comprising: performing anupdated MRI scan in which at least the tool tip is located.
 8. Themethod of claim 7, further comprising: displaying an updated location ofat least the tool tip based on the updated MRI scan.
 9. The method ofclaim 1, wherein the multiple joints comprise a first roll joint coupledto the first yaw joint and the second yaw joint, and a second roll jointcoupled to the second yaw joint and the third yaw joint.
 10. A method ofusing a surgical tool, comprising: receiving input from a master handcontroller; and driving a robotic arm based on the input received fromthe master hand controller, the robotic arm configured as a yaw planemanipulator and including: multiple joints and multiple degrees offreedom, the multiple joints including a first, second and third yawjoint, the yaw joints operatively linked by a plurality of roll joints;an MR-compatible structural material; multiple MR-compatible jointmotors; multiple MR-compatible joint encoders; and an end effectorholding a surgical tool.
 11. The method of claim 10, where the surgicaltool comprises bipolar forceps.
 12. The method of claim 10, where thesurgical tool comprises a suction tool.
 13. The method of claim 10,where the surgical tool comprises a micro-dissection tool.
 14. Themethod of claim 10, where the surgical tool comprises micro-scissors.15. The method of claim 10, where the driving comprises driving therobotic arm based on scaling the input and filtering the input to removehand tremor.
 16. The method of claim 10, where the surgical tool has atool tip, and the method further comprises: displaying a location of atleast the tool tip relative to an image from a magnetic resonanceimaging (MRI) scan, where the location of the tool tip relative to theimage from the MRI scan is determined based on positional data for therobotic arm that has been registered to the MRI scan using a digitizingtool.
 17. The method of claim 16, further comprising: performing anupdated MRI scan in which at least the tool tip is located.
 18. Themethod of claim 17, further comprising: calibrating the driving of therobotic arm against a position of the tool tip determined based on theupdated MRI scan.
 19. The method of claim 10, wherein the multiplejoints comprise a first roll joint coupled to the first yaw joint andthe second yaw joint, and a second roll joint coupled to the second yawjoint and the third yaw joint.
 20. A method of operating a surgicalsystem comprising one or more robotic arms, the method comprising:obtaining a magnetic resonance imaging (MRI) scan in which magneticresonance (MR) visible targets are located; registering positional datafor a robotic arm to the MRI scan using a digitizing tool, the roboticarm configured as a yaw plane manipulator and including: multiple jointsand multiple degrees of freedom, the multiple joints including a firstyaw joint, a second yaw joint and a third yaw joint, the yaw jointsoperatively linked by a plurality of roll joints; an MR-compatiblestructural material; multiple MR-compatible joint motors; multipleMR-compatible joint encoders; and an end effector configured for holdingan MR-compatible surgical tool; determining a location of the surgicaltool relative to an MR image based on the positional data and signalsfrom the multiple MR-compatible joint encoders; and displaying at leasta portion of the surgical tool relative to the MR image.
 21. The methodof claim 20, further comprising: driving the MR-compatible joint motorsbased on input from an operator.
 22. The method of claim 21, furthercomprising filtering the input to reduce effects of hand tremor.
 23. Themethod of claim 21, further comprising scaling the input.
 24. The methodof claim 21, further comprising: performing an updated MRI scan in whichat least a portion of the surgical tool is located.
 25. The method ofclaim 24, further comprising: calibrating the driving of the robotic armagainst a position of at least a portion of the surgical tool determinedbased on the updated MRI scan.
 26. The method of claim 24, furthercomprising: displaying at least a portion of the surgical tool based onthe updated MRI scan.
 27. The method of claim 20, wherein the roboticarm has six degrees of freedom.
 28. The method of claim 20, wherein themultiple joints comprise a first roll joint coupled to the first yawjoint and the second yaw joint, and a second roll joint coupled to thesecond yaw joint and the third yaw joint.
 29. A method of operating asurgical system comprising one or more robotic arms, the methodcomprising: obtaining a magnetic resonance imaging (MRI) scan in whichmagnetic resonance (MR) visible targets are located; registeringpositional data for a robotic arm to the MRI scan, the robotic armconfigured as a yaw plane manipulator and including: multiple joints andmultiple degrees of freedom, the multiple joints including a first yawjoint, a second yaw joint and a third yaw joint, the yaw jointsoperatively linked by a plurality of roll joints; an MR-compatiblestructural material; multiple MR-compatible joint motors; multipleMR-compatible joint encoders; and an end effector configured for holdingan MR-compatible surgical tool; determining a location of the surgicaltool relative to an MR image based on the positional data and signalsfrom the multiple MR-compatible joint encoders; and displaying at leasta portion of the surgical tool relative to the MR image.
 30. The methodof claim 29, further comprising: driving the MR-compatible joint motorsbased on input from an operator.
 31. The method of claim 29, wherein therobotic arm has six degrees of freedom.
 32. The method of claim 29,wherein the multiple joints comprise a first roll joint coupled to thefirst yaw joint and the second yaw joint, and a second roll jointcoupled to the second yaw joint and the third yaw joint.